Construct comprising metalized dicyclopentadiene polymer and method for producing same

ABSTRACT

The present invention comprises a method of forming a thin metal layer on a dicyclopentadiene polymer surface and to constructs comprising the metalized layer.

FIELD

This invention relates to constructs comprising a metalized dicyclopentadiene polymer surface and to methods of preparing such.

BACKGROUND

Metalized films are a well-established presence in the modern world. They are used for decorative purposes such as balloons, holographic images, light-reflecting decals, mirrored surfaces, sport cards and the like. They also are useful in packaging of processed fruits and vegetables, beverages, snack food, coffee and tobacco products due to their resistance to permeation by oxygen and moisture. They also can serve as insulators to keep heat and cold in, as in thermos applications, and to keep heat in and cold and radiation out as in space suit applications. In the electronics industry, metalized films find use in capacitors, resistors and other components.

With regard to pressure vessels, metalized polymeric surfaces could have substantial utility due to the above-mentioned barrier-enhancing properties. That is, metallization of a pressure vessel's polymeric liner could greatly improve the impermeability of the liner to fluids contained in the pressure vessel. This would be of particular value when dealing with modern lightweight pressure vessels comprised almost entirely of polymeric material.

As a non-limiting example, a so-called Type IV pressure vessel comprises a polymeric liner that is fully wrapped with a filamentous composite, which composite wrap provides the entire strength of the vessel. Type IV vessels are the lightest of the four currently approved classes of pressure vessel but are also the most expensive.

It is for obvious reasons preferable that the liner of a Type IV pressure vessel be as impermeable as possible to the fluid contained therein. While current polymers suitable for use as pressure vessel liners have differing degrees of impermeability, some of which are very good, metalizing the inner surface of the liner would be expected to further enhance impermeability.

Ancillary benefits that would flow from metallization of polymeric pressure vessel liners include increased inertness, i.e. lack of chemical reactivity, of the liner to contained pressurized fluids and improved insulating properties.

These benefits would, of course, inure to any type of pressure vessel that comprises a polymeric liner.

The problem with metalizing polymeric liners of pressure vessels is the current method of preparing them.

The virtually universal method of creating metalized polymer constructs is vacuum metallization. Vacuum metallization comprises placing the construct to be metalized into a vacuum chamber along with a hot ingot of the metal to be coated on the construct. An electromagnetic field in the chamber directs ions that are thermally released from the metal surface onto the construct. This process is, obviously, adequate for preparing metalized polymeric constructs in which the construct to be metalized is relatively small such that an appropriately sized vacuum chamber can be reasonably made. A problem arises, however, when applying this technique to pressure vessels, in particular to those vessels intended for the marine transport of compressed fluids, is contemplated. This is because those vessels are much larger.

With regard to the marine transport of fluids such as compressed natural gas (CNG), the economics of the manufacturing method, an ultimately the transportation method, is critical. Ocean-going vessels can carry just so much laden weight and the cost of shipping by sea reflects this fact, the cost being calculated on the total weight being shipped, that is, the weight of the product plus the weight of the container vessel in which the product is being shipped. If the net weight of the product is low compared to the tare weight of the shipping container, the cost of shipping per unit mass of product becomes prohibitive. This is particularly true of the transport of compressed fluids, which conventionally are transported in steel cylinders that are extremely heavy compared to weight of contained fluid.

This problem has been ameliorated somewhat by the advent of Type III and Type IV pressure vessels. Type III pressure vessels are comprised of a relatively thin metal liner that is wound with a filamentous composite wrap, which results in a vessel with the strength of a steel vessel at a substantial saving in overall vessel weight. Type IV pressure vessels, as mentioned previously, comprise a polymeric liner that is likewise wrapped with a composite filamentous material.

The use of Type III and Type IV vessels coupled with the trend to make these vessels very large—cylindrical vessels 18 meters in length and 2.5-3.0 meters in diameter are currently being fabricated and vessels 30 or more meters in length and 6 or more meters in diameter are contemplated—has resulted in a major step forward in optimizing the economics of ocean transport of compressed fluids.

As should be readily apparent, the difficulty and expense of creating vacuum chambers capable of enclosing pressure vessels of such enormous dimensions would be, to say the least, prohibitive.

What would be desirable, then, would be a method of metalizing polymeric surfaces that does not involve vacuum metallization. The instant invention provides such method and constructs prepared using the method.

SUMMARY

Thus, in one aspect, the instant invention relates to a construct, comprising:

at least one exposed surface that comprises a cyclopentadiene polymer; and

a thin layer of a first metal contiguous to and in contact with the cyclopentadiene polymer.

The construct may also comprise a thin layer of a second metal contiguous to and in contact with the thin layer of the first metal.

In an aspect of this invention the cyclopentadiene polymer comprises poly(cyclopentadiene) homopolymer.

In an aspect of this invention, the poly(cyclopentadiene) homopolymer is formed by ring-opening metathesis polymerization (ROMP) of cyclopentadiene.

In an aspect of this invention, the cyclopentadiene polymer is a copolymer of cyclopentadiene and one or more reactive ethylene monomers, wherein the mol % of cyclopentadiene in the copolymer is sufficient to maintain adhesion of the first metal to the cyclopentadiene polymer.

In an aspect of this invention, the first metal is selected from the group consisting of silver, gold, copper, nickel, tin, chromium, cadmium, zinc, cobalt and alloys thereof.

In an aspect of this invention, the first metal is silver.

In an aspect of this invention, the second metal is selected from the group consisting of aluminum, nickel, zinc, chromium, tin, copper and alloys thereof.

In an aspect of this invention, the second metal is selected from the group consisting of nickel and zinc.

In an aspect of this invention, the entire construct comprises a polycyclopentadiene polymer.

In an aspect of this invention, the cyclopentadiene polymer comprises a layer disposed over a construct body made of a material other than cyclopentadiene polymer but that is capable of adhering to cyclopentadiene polymer.

The construct may be a liner of a pressure vessel.

The construct may be a component of a pressure vessel.

The pressure vessel may be for containing CNG. CNG may be contained at a pressure of up to, or in excess of, 250 bar.

The pressure vessel may have a length in excess of 6 m.

The pressure vessel may have a diameter in excess of 1 m.

An aspect of this invention is a method comprising

providing a construct comprising at least one exposed surface comprising a dicyclopentadiene polymer;

cleaning the cyclopentadiene polymer surface with solvent but not otherwise activating the surface;

contacting the cyclopentadiene polymer surface with an aqueous solution comprising a salt of a first metal and a complexing agent;

contacting the aqueous solution of the complexed first metal at the cyclopentadiene polymer surface with an aqueous solution of a reducing agent wherein a layer of the first metal is deposited on surface.

The method may additionally comprise contacting the layer of first metal with an aqueous solution of a salt of a second metal; wherein

the second metal is deposited onto the first metal layer electrolytically or electrolessly.

In an aspect of the method of this invention, depositing the second metal electrolessly comprises contacting an aqueous solution of the second metal salt and a second complexing agent with an aqueous solution of a reducing agent at the surface of the first metal layer.

In an aspect of the method of this invention, electrolytically depositing the second metal onto the first metal comprises applying a negative electrical potential to the first metal layer; contacting the negatively-charged first metal layer with a positively-charged aqueous solution of the salt of the second metal, an electrode made of the second metal or a combination thereof.

In an aspect of the method of this invention, contacting the cyclopentadiene polymer with an aqueous solution comprising a complexed salt of the first metal comprises spraying the aqueous solution onto the cyclopentadiene polymer surface.

In as aspect of method of this invention, contacting the aqueous solution of the complexed salt of a first metal at the dicyclopentadiene polymer surface with an aqueous solution of a reducing agent comprises simultaneously spraying the two aqueous solutions onto the surface of the cyclopentadiene polymer surface.

In an aspect of the method of this invention, applying a negative electrical charge to the first metal layer and a positive electrical charge to the aqueous solution of the salt of the second metal comprises using a battery or a rectifier.

In an aspect of the method of this invention, contacting the negatively-charged first metal layer with the positively-charged aqueous solution of the salt of the second metal comprises spraying the positively-charged aqueous solution of the salt of the second metal onto the negatively-charged first metal surface.

In an aspect of the method of this invention, the first metal is selected from the group consisting of silver, copper, nickel, tin, chromium, cadmium, zinc, cobalt and mixtures or alloys thereof.

In an aspect of the method of this invention, the first metal is silver.

In an aspect of the method of this invention, the second metal is selected from the group consisting of nickel, zinc, chromium, tin and copper.

In an aspect of the method of this invention , the second metal is selected from the group consisting of nickel and zinc.

In an aspect of the method of this invention, the exposed surface that comprises a cyclopentadiene polymer is a liner of a pressure vessel.

In an aspect of the method of this invention, the liner has a rough-textured surface.

In an aspect of the method of this invention, the liner has a smooth-textured surface.

The method may be used to produce the construct previously described.

DETAILED DESCRIPTION Discussion

It is understood that, with regard to this description and the appended claims, any reference to any aspect of this invention made in the singular includes the plural and vice versa unless it is expressly stated or unambiguously clear from the context that such is not intended.

As used herein, any term of approximation such as, without limitation, near, about, approximately, substantially, essentially and the like, means that the word or phrase modified by the term of approximation need not be exactly that which is written but may vary from that written description to some extent. The extent to which the description may vary will depend on how great a change can be instituted and have one of ordinary skill in the art recognize the modified version as still having the properties, characteristics and capabilities of the word or phrase unmodified by the term of approximation. In general, but with the preceding discussion in mind, a numerical value herein that is modified by a word of approximation may vary from the stated value by ±10%, unless expressly stated otherwise.

As used herein, the term “optional,” “optionally” and the like refers to a feature of a construct or a step in a method that may, but need not necessarily, be present to achieve the objective of the construct design or of the method.

As used herein, “contiguous” refers to two surfaces that are adjacent and that are in direct contact or that would be in direct contact were it not for an intervening layer of another material.

As used herein, “impermeable” or “impervious” refers to the property of a substance that renders it substantially impossible for a fluid to penetrate to any significant degree into a surface formed of the first substance.

As used herein, “inert” refers to the property of a substance that renders a surface formed of the substance chemically unreactive toward any components of a fluid that may be contacted with the surface.

As used herein, the use of “preferred,” “preferably,” or “more preferred,” and the like refers to preferences as they existed at the time of filing of this patent application.

As used herein, a “fluid” refers to a gas, a liquid or a mixture of gas and liquid. For example, without limitation, natural gas as it is extracted from the ground and transported to a processing center is often a mixture of the gas with liquid contaminants. Such mixture would constitute a fluid for the purposes of this invention.

As used herein, a “construct” refers to any object of any design or physical form that can be fabricated from a dicyclopentadiene polymer or any material to which a dicyclopentadiene polymer can be adhered as a coating layer, either directly or by means of an intervening primer layer. A “base construct” refers to a construct to which the metallization method of this invention is to be applied. A base construct may itself comprise primarily dicyclopentadiene polymer or it may comprise some other material entirely, such as, without limitation, another polymer, a metal, a composite or a ceramic material.

As used herein, a “dicyclopentadiene polymer” refers to a polymer prepared by polymerization or curing (the terms are used interchangeably herein) of DCPD to yield a DCPD homopolymer (poly(dicyclopentadiene), pDCPD) or curing of a prepolymer formulation comprising dicyclopentadiene (DCPD) that is at least 92% pure.

As used herein a “prepolymer formulation” refers a blend of at least 92% pure DCPD, with one or more reactive ethylene monomer(s), a polymerization initiator or curing agent plus any other desirable additives prior to curing.

As used herein, a reactive ethylene monomer refers to a molecule that contains at least one ethylenic, i.e., —C═C—, bond that is capable of reacting with DCPD under the polymerization conditions selected. Preferred at present are cyclic ethylenic monomer such as the norbornenes.

As used herein, a “thin layer” of a metal refers to a layer that ranges from essentially an atomic monolayer to a layer that is about 0.5 μm thick.

As used herein, a “cleaning solvent” refers to any liquid that will not dissolve or substantially swell the particular DCPD polymer used in a surface to be metalized but which can be used to remove unwanted substances from that surface. Such liquids include, without limitation, water, alcohols such as, without limitation, methanol, ethanol and isopropanol; ketones such as acetone and methyl ethyl ketone; hydrocarbons such as hexane, cyclohexane, benzene, toluene, etc. Since the scope of DCPD polymers useful for the fabrication of a construct is quite broad, it is not possible to list every conceivable solvent that may be used with the polymer without deleteriously affecting its surface but those skilled in the art will very easily be able to determine which solvents do and which solvents do not meet the criteria herein without undue experimentation.

“Not otherwise activating the surface” refers to the fact that a dicyclopentadiene polymer surface of this invention need not be treated in any manner other than simple solvent cleaning to remove physical and chemical contaminants. That is, such procedures as “tinning,” which is often used when mirroring of polymeric surfaces, and plasma activation need not be used with the dicyclopentadiene polymers of this invention when applying the first metal layer to the polymer.

Thus, in an aspect of this invention, a construct is fabricated of a DCPD polymer or any material that a DCPD polymer can be adhered to or can be made to adhere to using an intervening primer layer. A primer layer refers to a layer of material interspersed between two other materials where the primer is capable of adhering to both materials, thus binding the two materials together. In the context of this invention, a primer would have to be able to adhere to whatever material a construct is made of and to the DCPD polymer that will eventually be metalized. Thus, if a base construct is other than a DCPD polymer, the DCPD polymer is applied to the construct as a coating to form a layer of the polymer on the exposed surface(s) of the construct wherein the exposed surfaces may have to be primed for the DCPD polymer to adhere.

If the base construct material is a dicyclopentadiene polymer or other polymeric material, the construct can be fabricated by any means available to those skilled in the art for such fabrications including, without limitation, casting, molding or carving from a solid block of the polymer.

Other materials of which the base construct can be fabricated include, without limitation, metals, composites, ceramics and the like.

The DCPD will be applied to the base construct as a layer, either directly or, as mentioned above, with the intervention of a primer layer.

The technique of metalizing certain materials has, of course, long been known. For example the silvering of glass to create mirrors has been used for over a century. The process involves the formation of an aqueous silver-ammonia complex from silver nitrate and ammonium hydroxide. The complex is contacted with a glass surface and with a second solution of a reducing agent that reduces the silver complex to elemental silver, which is deposited on the glass. The ancient technique, however, has consistently been found not to work with organic polymers. Therefore, as mentioned previously, the technique of metalizing organic polymeric surfaces using vacuum metallization has become the de facto standard.

It has now been unexpectedly and surprisingly found that the age-old, simple, inexpensive metallization technique works extremely well with dicyclopentadiene polymers.

Since the technique for metallization of glass and other non-organic polymer surfaces is well-known, it need only be described in brief.

As is readily gleaned from the above description of glass metallization to form mirrors, electroless deposition of a metal generally requires (1) a source of metal ions; (2) a complexing agent to keep the metal ions in stable solution; and (3) a reducing agent. The most well-known example is, of course, the above-mentioned glass silvering process in which silver nitrate provides the metal ions, ammonium hydroxide provides the complexing agent and a variety of substances such as, without limitation, the so-called “reducing sugars,” i.e., without limitation, glucose, fructose, glyceraldehydes and galactose and other aldehydes such as, without limitation, formaldehyde, provide the reducing agent. The choice of reducing agent depends on the metal salt being reduced; such selection is well within the knowledge of those skilled in the art and all such substances are within the scope of this invention.

pH adjustment of the solution(s) may be required but such is likewise well within the knowledge of those skilled in the art.

Many metals other than silver may be deposited using the above electroless process including, without limitation, gold, copper, nickel, chrome, cobalt, cadmium, iron, rhodium and tin. Alloys such as, without limitation, nickel-phosphorus, nickel-cobalt and nickel-X-phosphorus, where X is a third metal, can also be deposited.

Each may require its own complexing agent and, in particular, its own reducing agent. Complexing agents in addition to ammonium hydroxide include, without limitation, tetraaza compounds, ethylenediaminetetraacetic acid, citrates, tartrates, nitrilotriacetic acid and its alkali salts, gluconates and triethylamine.

Reducing agents, in addition to those mentioned above with regard to silver, include, without limitation, tartrates, dimethylamineborane, potassium borohydrides, sodium hypophosphite, thiosulfates, hydrazines, hydroxyamines and glyoxylic acid.

The selection of a suitable complexing agent and suitable reducing agent is well within the ability of those skilled in the art based on the disclosure herein and any such combination of complexing agent and reducing agent is within the scope of this invention.

In the practice of an embodiment of this invention, a DCPD polymer construct or a construct of another material which has been coated with a layer of DCPD polymer is first washed with one or more solvents to remove extraneous contaminants, such as dirt, oils, moisture and the like. No further treatment of the dicyclopentadiene polymer surface is required.

The cleaned DCPD polymer surface is then contacted with a solution of a salt of a first metal in the presence of a complexing agent to keep the metal ions in solution and to stabilize the solution generally. For the purpose of this invention, a metal salt and complexing agent solution may be referred to simply as the “complexed (first or second) metal salt” or “complex of the (first or second) metal salt.”

The surface with the complexed metal salt in contact with it or at least near the surface is simultaneously or consecutively contacted with an aqueous solution of a reducing agent. The metal complex is reduced to afford the zero valence metal which adheres to the DCPD polymer; i.e., an electrolessly deposited layer of metal on the surface results.

In an embodiment of this invention, the metal complex solution and the reducing solution can be concurrently sprayed onto the DCPD polymer surface either from separate spray units, the spray streams being directed so as to intersect at or near the DCPD polymer surface, or from a single spray unit having separate reservoirs and spray tip orifices, the two streams being mixed as they emerge from the spray tip and impinge on the polymer surface.

The surface that results from the deposition of the first metal may be rough-textured or smooth-textured depending on the texture of the construct, for instance, the interior surface of a pressure vessel liner may be smooth, which will result in an essentially mirrored surface, or rough, which will result in a rough-textured metalized surface.

The DCPD polymer surface metalized with the first metal may be used as such or it may be subjected to further deposition of a second metal.

The second metal may be disposed on the first metal by the same electroless process describe above or it may be deposited in an electrochemical process since the first metal provides the necessary conductivity for electrodeposition.

The electrodeposition process contemplated herein is well-known in the art and need not be extensively described. In brief, the metalized surface of the previously electrolessly plated DCPD construct is connected to the negative terminal (cathode) of a direct current power source, which may simply be a battery but, more commonly, is a rectifier. The anode, which constitutes the second metal to be deposited onto the first metal layer, is connected to the positive terminal (anode) of the power source. The anode and cathode are electrically connected by means of an electrolyte solution in which the surface to be metalized a second time is submersed or bathed as by contact with a spray of the solution.

The electrolyte solution contains dissolved metal salts of the metal to be plated as well as other ions that render the electrolyte conductive.

When power is applied to the system, the metallic anode is oxidized to produce cations of the metal to be deposited and the positively charged cations migrate to the cathode, i.e., the metallized surface of the DCPD polymer construct, where they are reduced to the zero valence state metal and are deposited on the construct.

In an embodiment of this invention, a solution of cations of the metal to be deposited can be prepared and the solution can be sprayed onto the metalized construct.

A presently preferred use of the method of this invention is the metallization of the interior surface of a DCPD polymer liner of a pressure vessel. The metallization of the DCPD polymer liner enhances the impermeability of the liner to a fluid that may be contained in the vessel as well as improving the inertness of the liner to reaction with any components of the fluid.

As a non-limiting example, a pressure vessel with a metalized DCPD liner can be used for the containment and transport of compressed natural gas, CNG. While pure CNG is a relatively unreactive fluid, it is most often transported from its source as raw natural gas. Raw gas refers to natural gas as it comes, unprocessed, from a well. This fluid contains, of course, natural gas (methane) itself but also often contains liquids such as condensate, natural gasoline and liquefied petroleum gas. Water may also be present. Other gases, either as such or dissolved in the water may also be present. These other gasses include nitrogen, carbon dioxide, hydrogen sulfide and helium. Some of these may be reactive in their own right or may be reactive when dissolved in water, such as carbon dioxide which produces an acid when dissolved in water.

While DCPD liners exhibit a fairly high degree of imperviousness and inertness to the components of raw gas, metalizing the surface of the PDCD can greatly enhance these properties. A method of metalizing the inside of a pressure vessel is therefore highly beneficial in that the enhanced performance is achieved with minimal change in the mass of the pressure vessel—the thickness of the metalized surface will be minimal.

In the present example, the pressure vessels described herein can carry a variety of gases, such as raw gas straight from a bore well, including raw natural gas, e.g. when compressed—raw CNG or RCNG, or H₂, or CO₂ or processed natural gas (methane), or raw or part processed natural gas, e.g. with CO₂ allowances of up to 14% molar, H₂S allowances of up to 1,000 ppm, or H₂ and CO₂ gas impurities, or other impurities or corrosive species. The preferred use, however, is CNG transportation, be that raw CNG, part processed CNG or clean CNG—processed to a standard deliverable to the end user, e.g. commercial, industrial or residential.

CNG can include various potential component parts in a variable mixture of ratios, some in their gas phase and others in a liquid phase, or a mix of both. Those component parts will typically comprise one or more of the following compounds: C₂H₆, C₃H₈, C₄H₁₀, C₅H₁₂, C₇H₁₆, C₈H₁₈C₉+ hydrocarbons, CO₂ and H₂S, plus potentially toluene, diesel and octane in a liquid state, and other impurities/species.

These and other features of the present invention may be used independently or in combination, within the scope of the claims and/or the present disclosure.

The present invention has therefore been described above purely by way of example. Modifications in detail may be made to the invention within the scope of the claims appended hereto. 

1. A method, comprising: providing a base construct having at least one surface that comprises a dicyclopentadiene polymer; cleaning the dicyclopentadiene polymer surface with solvent but not otherwise activating the surface; providing a first aqueous solution comprising a salt of a first metal and a complexing agent that forms a complex with the first metal; and contacting the first aqueous solution at or near the dicyclopentadiene polymer surface with a second aqueous solution comprising a reducing agent whereby a layer of the first metal is deposited onto the dicyclopentadiene surface.
 2. The method of claim 1, wherein the base construct is fabricated of a dicyclopentadiene polymer such that the at least one surface is a surface of the base construct itself.
 3. The method of claim 1, wherein the base construct is fabricated of a material other than a dicyclopentadiene polymer such that the at least one surface comprises a layer of a dicyclopentadiene polymer disposed over a surface of the base construct.
 4. The method of claim 1, wherein contacting the first aqueous solution with the second aqueous solution at or near the dicyclopentadiene polymer surface comprises simultaneously spraying the two aqueous solutions at the dicyclopentadiene polymer surface such that the sprays mix on or near the surface.
 5. The method of claim 1, wherein a second metal layer is disposed over the first metal layer electrolytically or electrolessly.
 6. The method of claim 5, wherein depositing the second metal electrolessly on the first metal comprises contacting, at or near the first metal layer surface, a third aqueous solution comprising a salt of the second metal and a complexing agent with a fourth aqueous solution comprising a reducing agent.
 7. The method of claim 6, wherein contacting the third and fourth solutions comprises spraying the two aqueous solutions at the dicyclopentadiene polymer surface such that the sprays mix on or near the surface.
 8. The method of claim 5, wherein electrolytically depositing the second metal onto the first metal comprises: contacting a negative terminal of a direct current power supply with the first metal layer; providing an aqueous solution comprising a salt of the second metal, an electrode made of the second metal immersed in the aqueous solution or a combination thereof; contacting a positive terminal of the direct current power supply with the aqueous solution; contacting the first metal layer with the aqueous solution; and turning on the power supply.
 9. The method of claim 8, wherein contacting the first metal layer with the aqueous solution comprises spraying the aqueous solution onto the first metal layer.
 10. The method of claim 8, wherein contacting the first metal layer with the aqueous solution comprises dipping the first metal layer into the aqueous solution.
 11. The method of claim 8, wherein the negative and positive terminals of a direct current power supply comprise a battery or a rectifier.
 12. The method of claim 5, wherein the second metal is selected from the group consisting of nickel, zinc, chromium, tin and copper.
 13. The method of claim 5, wherein the second metal is selected from the group consisting of nickel and zinc.
 14. The method of claim 1, wherein the first metal is selected from the group consisting of silver, copper, nickel, tin, chromium, cadmium, zinc, cobalt and mixtures or alloys thereof.
 15. The method of claim 14, wherein the first metal is silver.
 16. A metalized construct made using the method of claim
 1. 17. The metalized construct of claim 16, comprising a metalized polymeric liner for a pressure vessel.
 18. The construct of claims 17, wherein the metal layer on the polymeric liner is smooth textured or rough-textured. 19.-21. (canceled)
 22. A pressure vessel comprising a construct according to claim
 16. 23. A pressure vessel according to claim 22, wherein the pressure vessel is suitable for containing CNG.
 24. A pressure vessel according to claim 23, having a length in excess of 6 m.
 25. A pressure vessel according to claim 23, having a diameter in excess of 1 m.
 26. A ship comprising one of more pressure vessels as defined in claim
 22. 